Semiconductor device

ABSTRACT

An electrostatic protection element whose electrostatic breakdown resistance can be adjusted with a required minimum design change is provided. 
     A semiconductor device includes an electrostatic protection element including a bipolar transistor whose base region and emitter region are electrically coupled together through a resistance region. At this time, the base region of the electrostatic protection element has a side including a facing portion that faces the collector region. The facing portion of the side includes an exposed portion that is exposed from an emitter wiring in plan view and a covered portion that is covered by the emitter wiring in plan view.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2016-186833 filed onSep. 26, 2016 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a semiconductor device. For example,the invention relates to a technique effective when applied to asemiconductor device having an electrostatic protection element.

Japanese Unexamined Patent Application Publication No. Hei06(1994)-232386 describes a technique in which a semiconductor chip isprevented from being broken by alleviating an electric field byincreasing a width of a field plate extending from a pn junction portionof the semiconductor chip to greater than that extending from a straightportion of the semiconductor chip in a corner portion of thesemiconductor chip.

SUMMARY

A semiconductor device is required to have an electrostatic breakdownresistance to prevent itself from being broken by static electricity.For this reason, the semiconductor device is provided with anelectrostatic protection element in order to improve the electrostaticbreakdown resistance.

Here, a design change of the electrostatic protection element of thesemiconductor device may be required to be performed to adjust theelectrostatic breakdown resistance. In this case, much labor and timeare required to design again the electrostatic protection element fromthe beginning, so that a structure of the electrostatic protectionelement whose electrostatic breakdown resistance can be adjusted with arequired minimum design change is desired.

The other problems and novel features will become apparent from thedescription of the present specification and the accompanying drawings.

A semiconductor device according to an embodiment includes anelectrostatic protection element including a bipolar transistor whosebase region and emitter region are electrically coupled together througha resistance region. At this time, the base region of the electrostaticprotection element has a first side including a facing portion thatfaces the collector region. The facing portion of the first sideincludes an exposed portion that is exposed from an emitter wiring inplan view and a covered portion that is covered by the emitter wiring inplan view.

According to the embodiment, it is possible to provide an electrostaticprotection element whose electrostatic breakdown resistance can beadjusted with a required minimum design change.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a circuit configuration example inwhich an electrostatic protection element according to a firstembodiment is provided in a previous stage of an input transistor.

FIG. 2 is a graph showing a waveform obtained by a TLP measuringinstrument.

FIG. 3A is a diagram for explaining a circuit operation of theelectrostatic protection element in a segment between A and B shown inFIG. 2. FIG. 3B is a diagram for explaining a circuit operation of theelectrostatic protection element in a segment between B and C shown inFIG. 2. FIG. 3C is a diagram for explaining a circuit operation of theelectrostatic protection element in a segment between C and D shown inFIG. 2. FIG. 3D is a diagram for explaining a circuit operation of theelectrostatic protection element in a segment between D and E shown inFIG. 2.

FIG. 4A is a schematic plan view showing components formed in asemiconductor substrate among components of an electrostatic protectionelement according to a related art. FIG. 4B is a schematic plan viewshowing not only the components formed in the semiconductor substratebut also components including a wiring layer formed over thesemiconductor substrate.

FIG. 5 is a cross-sectional view taken along line A-A in FIG. 4B.

FIG. 6 is a cross-sectional view taken along line B-B in FIG. 4B.

FIG. 7A is a schematic plan view showing components formed in asemiconductor substrate among components of the electrostatic protectionelement according to the first embodiment. FIG. 7B is a schematic planview showing components including also a wiring layer formed over thesemiconductor substrate.

FIG. 8 is a cross-sectional view taken along line A-A in FIG. 7B.

FIG. 9 is a cross-sectional view taken along line B-B in FIG. 7B.

FIG. 10A is a schematic plan view showing components formed in asemiconductor substrate among components of an electrostatic protectionelement according to a second embodiment. FIG. 10B is a schematic planview showing components including also a wiring layer formed over thesemiconductor substrate.

FIG. 11 is a cross-sectional view showing a schematic device structureof an electrostatic protection element according to a modified example.

DETAILED DESCRIPTION

The following embodiments will be explained, divided into pluralsections or embodiments, if necessary for convenience. Except for thecase where it shows clearly in particular, they are not mutuallyunrelated and one has relationships such as a modification, details, andsupplementary explanation of some or entire of another.

In the following embodiments, when referring to the number of elements,etc. (including the number, a numeric value, an amount, a range, etc.),they may be not restricted to the specific number but may be greater orsmaller than the specific number, except for the case where they areclearly specified in particular and where they are clearly restricted toa specific number theoretically.

Furthermore, in the following embodiments, it is needless to say that anelement (including an element step etc.) is not necessarilyindispensable, except for the case where it is clearly specified inparticular and where it is considered to be clearly indispensable from atheoretical point of view, etc.

Similarly, in the following embodiments, when shape, positionrelationship, etc. of an element etc. is referred to, what resembles oris similar to the shape substantially shall be included, except for thecase where it is clearly specified in particular and where it isconsidered to be clearly not right from a theoretical point of view.This statement also applies to the numeric value and range describedabove.

In all the drawings for explaining embodiments, the same symbol isattached to the same member, as a principle, and the repeatedexplanation thereof is omitted. In order to make a drawing intelligible,hatching may be attached even if it is a plan view.

First Embodiment

<Circuit Configuration of Electrostatic Protection Element>

An electrostatic protection element according to the first embodiment isassumed to be a “CB diode” including a bipolar transistor whose base andemitter are electrically coupled together through a resistor. Accordingto the “CB diode”, it is possible to flow charged electric charge to theground by a large collector current, so that it is possible to obtainadvantages that electrostatic breakdown resistance can be improved and arise in voltage based on the charged electric charge is suppressedbecause of snapback phenomenon.

FIG. 1 is a circuit diagram showing a circuit configuration example inwhich an electrostatic protection element CB according to the firstembodiment is provided in a previous stage of an input transistor Tr. Asshown in FIG. 1, the input transistor Tr including, for example, a PNPbipolar transistor is provided between a power supply terminal VCC towhich a power supply potential is supplied and a ground terminal GND towhich a ground potential (reference potential) is supplied.Specifically, the emitter of the input transistor Tr is electricallycoupled to the power supply terminal VCC and the collector of the inputtransistor Tr is electrically coupled to the ground terminal GND. Thebase of the input transistor Tr is electrically coupled to an inputterminal IN to which a signal is inputted.

Next, the electrostatic protection element CB according to the firstembodiment is provided in a previous stage of the input transistor Tr.Specifically, the electrostatic protection element CB according to thefirst embodiment is formed of a “CB diode” using, for example, an NPNbipolar transistor Q. The collector of the NPN bipolar transistor Q thatincludes the electrostatic protection element CB is electrically coupledto the input terminal IN and the emitter of the NPN bipolar transistor Qis electrically coupled to the ground terminal GND. On the other hand,the base of the NPN bipolar transistor Q is electrically coupled to theground terminal GND through an intentionally provided resistor R.Therefore, the emitter and the base of the NPN bipolar transistor Q thatincludes the electrostatic protection element CB are electricallycoupled together through the resistor R, and thereby the electrostaticprotection element CB including the “CB diode” is formed.

<Circuit Operation of Electrostatic Protection Element>

Subsequently, an operation of the electrostatic protection element CBaccording to the first embodiment will be described. In particular, inthe first embodiment, an operation of the electrostatic protectionelement CB when a plus surge charge enters the input terminal IN shownin FIG. 1 will be described. The operation of the electrostaticprotection element CB when a plus surge charge enters the input terminalIN will be described based on a waveform obtained by a TLP (TransmissionLINE Pulse) measuring instrument. FIG. 2 is a graph showing the waveformobtained by the TLP measuring instrument. In FIG. 2, the horizontal axisindicates a collector voltage of the electrostatic protection element CBand the vertical axis indicates a current flowing through the ground.The waveform obtained by the TLP measuring instrument is a waveformobtained by monitoring a collector voltage applied to the collector anda current flowing from the collector to the ground by applying a plussurge charge to the collector while gradually increasing the plus surgecharge by a 250 ns pulse. In particular, a current value flowing fromthe collector to the ground indicated by the vertical axis means acapacity for flowing the plus surge charge entering the input terminalIN from the input terminal IN to the ground terminal GND. That is, itmeans that the greater the current value flowing from the collector tothe ground is, the higher the capacity of the electrostatic protectionelement CB that flows the plus surge charge entering the input terminalIN to the ground is. In other words, it means that the greater thecurrent value flowing from the collector to the ground is, the more theelectrostatic breakdown resistance of the electrostatic protectionelement CB can be improved, and thereby it is possible to effectivelyprotect the input transistor Tr shown in FIG. 1 from electrostaticbreakdown.

(1) Operation in a Segment Between A and B in FIG. 2

First, an operation in a segment between A and B in FIG. 2 will bedescribed. In the segment between A and B shown in FIG. 2, a collectorvoltage is applied to the collector of the NPN bipolar transistor Q thatincludes the electrostatic protection element CB by the plus surgecharge entering the input terminal. Here, FIG. 3A is a diagram forexplaining a circuit operation of the electrostatic protection elementCB in the segment between A and B shown in FIG. 2. In the NPN bipolartransistor Q, a pn junction is formed between the collector (n-typesemiconductor region) and the base (p-type semiconductor region) and areverse bias is applied to the pn junction when the plus surge charge isapplied to the collector. However, as shown in FIG. 3, the collectorvoltage is smaller than a reverse junction breakdown voltage of the pnjunction, so that no leakage current occurs in the pn junction. Thecollector voltage at this time needs to be higher than a voltage used bya product. This is because if the collector voltage in the segmentbetween A and B is lower than the voltage used by a product, a leakagecurrent occurs when the voltage used by a product is applied to theinput terminal.

(2) Operation in a Segment Between B and C in FIG. 2

Subsequently, an operation in a segment between B and C in FIG. 2 willbe described. In the segment between B and C shown in FIG. 2, the plussurge charge is more accumulated at the input terminal than in thesegment between A and B shown in FIG. 2. As a result, a large collectorvoltage is applied to the collector of the NPN bipolar transistor Q thatincludes the electrostatic protection element CB. FIG. 3B is a diagramfor explaining a circuit operation of the electrostatic protectionelement CB in the segment between B and C shown in FIG. 2. Also in thiscase, a reverse bias is applied to the pn junction formed by thecollector and the base of the NPN bipolar transistor Q. Here, as shownin FIG. 3B, the collector voltage is greater than the reverse junctionbreakdown voltage of the pn junction. As a result, the pn junction isbroken down, and thereby a leakage current occurs between the collectorand the base. The leakage current flows in a route ofcollector→base→resistor R→ground.

(3) Operation in a Segment Between C and D in FIG. 2

Next, an operation in a segment between C and D in FIG. 2 will bedescribed. As shown in FIG. 3B, the leakage current flows in the routeof the collector of the NPN bipolar transistor Q→the base→the resistorR→the ground. As a result, the voltage of the resistor R drops. As aresult, a potential difference occurs between the emitter and the baseof the NPN bipolar transistor Q. Specifically, a base voltage applied tothe base of the NPN bipolar transistor Q becomes higher than an emittervoltage applied to the emitter of the NPN bipolar transistor Q. Thereby,as shown in FIG. 3C, a forward bias is applied to the pn junctionbetween the base (p-type semiconductor region) and the emitter (n-typesemiconductor region) of the NPN bipolar transistor Q, and a currentflows from the base to the emitter of the NPN bipolar transistor Q. Apoint at which a current starts to flow in a route of the collector ofthe NPN bipolar transistor Q→the base→the emitter→the ground in this wayis a point C shown in FIG. 2, and thereafter the collector voltagedrops. This is because a current path of collector→base→emitter→groundshown in FIG. 3C has a resistance lower than that of a current path ofcollector→base→resistor R→ground shown in FIG. 3B.

(4) Operation in a Segment Between D and E in FIG. 2

Subsequently, an operation in a segment between D and E in FIG. 2 willbe described. As shown in FIG. 3C, a current flows in the route of thecollector of the NPN bipolar transistor Q→the base→the emitter→theground. As a result, the NPN bipolar transistor Q turns on. Thereby, asshown in FIG. 3D, a large current flows from the collector to theemitter of the NPN bipolar transistor Q. Thereby, according to theelectrostatic protection element CB of the first embodiment, it possibleto flow the plus surge charge entering the input terminal IN to theground terminal GND.

A point E in FIG. 2 is a point over which a current cannot be flown as aresult that any part of the electrostatic protection element CB isbroken by a large current flowing from the collector to the emitter, andthe point E indicates an allowable current ability (an ability to flow acurrent) of the electrostatic protection element CB. In other words,when the amount of current when the plus surge charge that has enteredthe input terminal IN is flown to the ground terminal GND is within arange of the allowable current ability of the electrostatic protectionelement CB, it is possible to flow the plus charge that has entered theinput terminal IN to the ground terminal GND without breaking theelectrostatic protection element CB. On the other hand, when the amountof current when the plus charge that has entered the input terminal INis flown to the ground terminal GND exceeds the range of the allowablecurrent ability of the electrostatic protection element CB, the point Eshown in FIG. 2 is reached and the electrostatic protection element CBis broken. Therefore, the electrostatic breakdown resistance of theelectrostatic protection element CB is determined based on the point Eshown in FIG. 2.

In the operation described above, a case in which the plus surge chargeis applied to the input terminal IN is described. However, for example,when a minus surge charge is applied to the input terminal IN, theelectrostatic protection element CB operates as described below. Forexample, when a minus surge charge is applied to the collector of theNPN bipolar transistor Q in FIG. 3B, a forward bias is applied to the pnjunction between the collector and the base of the NPN bipolartransistor Q. As a result, the minus surge charge flows from thecollector to the base of the NPN bipolar transistor Q and then flows tothe ground terminal GND through the resistor R. Thereby, according tothe electrostatic protection element CB of the first embodiment, evenwhen a minus surge charge enters the input terminal IN, the minus surgecharge can be flown to the ground terminal GND.

<Characteristics Required by Electrostatic Protection Element>

Regarding the electrostatic protection element CB, for example, when theamount of surge charge which causes the collector voltage (surgevoltage) to be higher than a voltage used by a product enters the inputterminal IN, it is important to turn on the NPN bipolar transistor Qthat includes the electrostatic protection element CB in a state inwhich the amount of accumulated surge charge is as small as possible andcauses the surge charge accumulated in the collector (input terminal IN)to flow to the ground terminal GND by a large current that flows fromthe collector to the emitter of the NPN bipolar transistor Q. This isbecause when the NPN bipolar transistor Q that includes theelectrostatic protection element CB does not turn on, the amount ofsurge charge flowing from the collector to the ground terminal GND issmall, so that the surge charge is accumulated in the input terminal IN,and thereby there is a risk that the input transistor Tr (see FIG. 1)coupled to the input terminal IN is broken by a large collector voltage(surge voltage) caused by the surge charge.

Therefore, in the electrostatic protection element CB, it is importantto turn on the NPN bipolar transistor Q that includes the electrostaticprotection element CB in a state in which the amount of accumulatedsurge charge is as small as possible. This means that it is important tochange the state shown in FIG. 3B to the state shown in FIG. 3C evenwhen the amount of surge charge is small. In other words, it isimportant to cause the electrostatic protection element CB to snap backeven when the amount of surge charge is as small as possible.

Here, in a state shown in FIG. 3B, when a voltage determined by aproduct of a resistance value of the resistor R and a current value of aleakage current flowing through the resistor R reaches a snapbackvoltage, the state proceeds to a state of FIG. 3C. At this time, forexample, if the resistance value of the resistor R is small even whenthe current value of the leakage current is increased, the voltagedetermined by the product of the resistance value of the resistor R andthe current value of the leakage current flowing through the resistor Rbecomes smaller than the snapback voltage (a voltage between the baseand the emitter when the NPN bipolar transistor Q turns on, in otherwords, a built-in potential between the base and the emitter of the NPNbipolar transistor Q). In other words, even when the current value ofthe leakage current is increased, if the resistance value of theresistor R is small, the NPN bipolar transistor Q does not turn on andthe surge charge does not flow efficiently from the input terminal IN tothe ground terminal GND. As a result, there is a risk that the inputtransistor Tr coupled to the input terminal IN is broken by a largecollector voltage (surge voltage) caused by the surge charge accumulatedin the input terminal IN.

On the other hand, even when the current value of the leakage current isnot so large, if the resistance value of the resistor R is large, thevoltage determined by the product of the resistance value of theresistor R and the current value of the leakage current flowing throughthe resistor R reaches the snapback voltage. Therefore, to cause thevoltage determined by the product of the resistance value of theresistor R and the current value of the leakage current flowing throughthe resistor R to reach the snapback voltage, it is necessary to adjusteach of the resistance value of the resistor R and the current value ofthe leakage current flowing through the resistor R in a good balance.

For example, in a semiconductor device, to realize an electrostaticprotection element CB that easily snaps back, it may be required toperform design change regarding the resistance value of the resister Rand the current value of the leakage current flowing through theresistor R. In this case, much labor and time are required to designagain the electrostatic protection element from the beginning, so that astructure of an electrostatic protection element that easily snaps backis desired with a required minimum design change.

Therefore, in the description below, first, a device structure of anelectrostatic protection element CB1 according to a related art will bedescribed. It will be described that in the related art, there is a roomfor improvement from a viewpoint of performing design change related tothe resistance value of the resister R and the current value of theleakage current flowing through the resistor R to realize anelectrostatic protection element CB that easily snaps back. Thereafter,a technical idea of the first embodiment in which improvement is appliedto the room for improvement in the related art will be described.

<Description of Related Art>

The “relate art” in the present specification is a technique having aproblem that is newly found by the inventors and is not a known relatedart. However, the “relate art” in the present specification is atechnique described intending a premise technique (unknown technique) ofnew technical idea.

FIGS. 4A and 4B are diagrams showing a device structure of theelectrostatic protection element CB1 according to the related art. Inparticular, FIG. 4A is a schematic plan view showing components formedin a semiconductor substrate among components of the electrostaticprotection element CB1 according to the related art. FIG. 4B is aschematic plan view further showing not only the components formed inthe semiconductor substrate among the components of the electrostaticprotection element CB1 according to the related art but also componentsincluding a wiring layer formed over the semiconductor substrate.

As shown in FIG. 4A, the electrostatic protection element CB1 accordingto the related art is formed inside an isolation region ISO in planview. Specifically, for example, an epitaxial layer EPI made of ann-type semiconductor layer is formed inside the isolation region ISO.Inside the epitaxial layer EPI, a collector region CR made of an n-typesemiconductor region and a base region BR made of a p-type semiconductorregion, which is separately facing the collector region CR, are formed.At this time, as shown in FIG. 4A, the base region BR has a protrudingportion PIP extending from a portion facing the collector region. Anemitter region ER made of an n-type semiconductor region is formed so asto be contained in the base region BR.

Next, as shown in FIG. 4B, in the electrostatic protection element CB1according to the related art, a collector wiring CWL made of, forexample, an aluminum wiring is formed in a position planarly overlappingwith the collector region CR. The collector region CR and the collectorwiring CWL are electrically coupled together by a plurality of plugsPLG1 arranged at equal intervals. The collector wiring CWL iselectrically coupled with, for example, the input terminal IN shown inFIG. 1.

The base region BR arranged in a position separately facing thecollector region CR has a side S1. The side S1 includes a facing portionFP facing the collector region CR. The facing portion FP of the side S1is a boundary line of a pn junction between the base region BR and theepitaxial layer EPI. For example, when a plus surge charge enters theinput terminal IN electrically coupled to the collector wiring CWL andthereby a voltage greater than or equal to the reverse junctionbreakdown voltage is applied between the collector region CR and thebase region BR, a leakage current occurs at the pn junction of thefacing portion FP.

Subsequently, in plan view, the emitter region ER is formed in aposition contained in the base region BR. An emitter wiring EWL made of,for example, an aluminum wiring is formed in a position planarlyoverlapping with the emitter region ER and partially overlapping withthe base region BR. The emitter wiring EWL is electrically coupled withthe emitter region ER by a plurality of plugs PLG2 arranged at equalintervals and is also electrically coupled with the base region BR by aplurality of plugs PLG3. Further, the emitter wiring EWL is electricallycoupled with, for example, the ground terminal GND shown in FIG. 1.Here, as shown in FIG. 4B, a region filled with oblique lines in thebase region BR functions as a resistance region RR1. Therefore, in theelectrostatic protection element CB1 according to the related art, theemitter region ER and the base region BR are electrically coupledtogether through the resistance region RR1.

In FIG. 4B, the leakage current shown in FIG. 3B flows in a current pathof (input terminal IN)→collector wiring CWL→plug PLG1→collector regionCR→epitaxial layer EPI→facing portion FP→base region BR→resistanceregion RR1→plug PLG3→emitter wiring EWL→(ground terminal GND).

Next, FIG. 5 is a cross-sectional view taken along line A-A in FIG. 4B.As shown in FIG. 5, the epitaxial layer EPI is formed over asemiconductor substrate 1S and the collector region CR is formed in apart of a surface region of the epitaxial layer EPI. In the epitaxiallayer EPI, the base region BR is formed in a part of the surface regionseparated from the collector region CR and the emitter region ER isformed so as to be contained in the base region BR.

An interlayer insulating film IL made of, for example, a silicon oxidefilm is formed over the epitaxial layer EPI. In the interlayerinsulating film IL, the plug PLG1 that penetrates the interlayerinsulating film IL and reaches the collector region CR is formed, andthe plug PLG2 that penetrates the interlayer insulating film IL andreaches the emitter region ER is formed. Further, over the interlayerinsulating film IL, the collector wiring CWL and the emitter wiring EWLare formed. The collector wiring CWL is electrically coupled with thecollector region CR through the plug PLG1. On the other hand, theemitter wiring EWL is electrically coupled with the emitter region ERthrough the plug PLG2.

Subsequently, FIG. 6 is a cross-sectional view taken along line B-B inFIG. 4B. As shown in FIG. 6, the base region BR is formed in a part ofthe surface region of the epitaxial layer EPI formed over thesemiconductor substrate 1S. The interlayer insulating film IL is formedover the epitaxial layer EPI in which the base region BR is formed. Inthe interlayer insulating film IL, the plug PLG3 that penetrates theinterlayer insulating film IL is formed. Over the interlayer insulatingfilm IL, the emitter wiring EWL is formed. The emitter wiring EWL iselectrically coupled with the base region BR through the plug PLG3. Atthis time, a region (a region filled with dots) formed in a positionnear the plug PLG3 functions as the resistance region RR1. In the waydescribed above, the electrostatic protection element CB1 according tothe related art is formed.

<Study for Improvement>

The inventors have studied the electrostatic protection element CB1according to the related art from a viewpoint of realizing a structureof an electrostatic protection element that easily snaps back with arequired minimum design change. As a result, it becomes clear that theelectrostatic protection element CB1 according to the related art has aroom for improvement, so that the room for improvement will bedescribed.

For example, to cause the electrostatic protection element CB1 to easilysnap back is the same as to be able to change the state shown in FIG. 3Bto the state shown in FIG. 3C. In FIG. 3B, to cause the voltagedetermined by the product of the resistance value of the resistor R andthe current value of the leakage current flowing through the resistor Rto easily reach the snapback voltage, it is necessary to adjust each ofthe resistance value of the resistor R and the current value of theleakage current flowing through the resistor R.

In this regard, in FIG. 4B that shows the device structure of theelectrostatic protection element CB1 according to the related art, theleakage current shown in FIG. 3B flows in a current path of (inputterminal IN)→collector wiring CWL→plug PLG1→collector regionCR→epitaxial layer EPI→facing portion FP→base region BR→resistanceregion RR1→plug PLG3→emitter wiring EWL→(ground terminal GND). Here, tocause the voltage determined by the product of the resistance value ofthe resistor R and the current value of the leakage current flowingthrough the resistor R to easily reach the snapback voltage, first, itis considered to increase the current value of the leakage current.However, for example, as shown in FIG. 4B, in the related art, theentire facing portion FP of the base region BR facing the collectorregion CR has been used as a portion where the leakage current occurs,so that it is difficult to further increase the leakage current.Therefore, the next idea is to increase the resistance value of theresistor R. However, this means that the size of the resistance regionRR1 shown in FIG. 4B is increased. This means that the size of theprotruding portion PTP of the base region BR shown in FIG. 4A isincreased. In this case, the size of the electrostatic protectionelement CB1 according to the related art is increased. For example, theelectrostatic protection element CB1 itself is an element irrelevant toa product operation of the semiconductor device itself, so that a designchange that increases the size of the electrostatic protection elementCB1 should be avoided because it is desired that the electrostaticprotection element CB1 has a required minimum occupancy area.

Further, changing the size of the base region BR itself means that adesign of a semiconductor area that is formed into a semiconductorsubstrate must be changed from the beginning, so that much labor andtime are required. Therefore, in the related art, from a viewpoint ofimproving the performance of the electrostatic protection element CB1,when making a design change to cause the voltage determined by theproduct of the resistance value of the resistor R and the current valueof the leakage current flowing through the resistor R to easily reachthe snapback voltage, the means that can be currently employed have adisadvantage of increasing the size of the electrostatic protectionelement CB1 and a disadvantage of requiring much labor and time for thedesign change. In other words, in the related art, there is a room forimprovement that it is difficult to improve the performance of theelectrostatic protection element CB1 without causing a disadvantage ofincreasing the size of the electrostatic protection element CB1 and adisadvantage of requiring much labor and time for the design change.

Therefore, in the first embodiment, improvement is applied to the roomfor improvement in the related art. Hereinafter, a technical idea of thefirst embodiment where the improvement is applied will be described withreference to the drawings.

<Device Structure of Electrostatic Protection Element>

FIGS. 7A and 7B are diagrams showing a device structure of theelectrostatic protection element CB according to the first embodiment.In particular, FIG. 7A is a schematic plan view showing componentsformed in a semiconductor substrate among components of theelectrostatic protection element CB according to the first embodiment.FIG. 7B is a schematic plan view showing components including also awiring layer formed over the semiconductor substrate among thecomponents of the electrostatic protection element CB according to thefirst embodiment.

As shown in FIG. 7A, the electrostatic protection element CB accordingto the first embodiment is formed inside an isolation region ISO in planview. Specifically, for example, an epitaxial layer EPI made of ann-type semiconductor layer is formed inside the isolation region ISO.Inside the epitaxial layer EPI, a collector region CR made of an n-typesemiconductor region and a base region BR made of a p-type semiconductorregion, which is separately facing the collector region CR, are formed.At this time, as shown in FIG. 7A, the base region BR has a protrudingportion PTP extending from a portion facing the collector region. Anemitter region ER made of an n-type semiconductor region is formed so asto be contained in the base region BR.

Next, as shown in FIG. 7B, in the electrostatic protection element CBaccording to the first embodiment, a collector wiring CWL made of, forexample, an aluminum wiring is formed in a position planarly overlappingwith the collector region CR. The collector region CR and the collectorwiring CWL are electrically coupled together by a plurality of plugsPLG1 arranged at equal intervals. The collector wiring CWL iselectrically coupled with, for example, the input terminal IN shown inFIG. 1.

Subsequently, as shown in FIG. 7B, in plan view, the emitter region ERis formed in a position contained in the base region BR. An emitterwiring EWL made of, for example, an aluminum wiring is formed in aposition planarly overlapping with the emitter region ER and partiallyoverlapping with the base region BR. The emitter wiring EWL iselectrically coupled with the emitter region ER by a plurality of plugsPLG2 arranged at equal intervals and is also electrically coupled withthe base region BR by a plurality of plugs PLG3. Further, the emitterwiring EWL is electrically coupled with, for example, the groundterminal GND shown in FIG. 1.

Here, the base region BR arranged in a position separately facing thecollector region CR has a side S1. The side S1 includes a facing portionFP facing the collector region CR. In other words, as shown in FIG. 7B,the side S1 of the base region BR includes the facing portion FP facingthe collector region CR. In the first embodiment, the facing portion FPincludes an exposed portion EXP that is exposed from the emitter wiringEWL and a covered portion CVP that is covered by the emitter wiring EWL.The side S1 of the base region BR includes one end portion covered bythe emitter wiring EWL in plan view and the other end portion exposedfrom the emitter wiring EWL in plan view. A plug PLG3 that electricallycouples the base region BR and the emitter region EWL together is formedin an end portion region of the base region BR including the one endportion of the side S1.

Next, as shown in FIG. 7B, a notch portion NT is formed in the emitterwiring EWL and the exposed portion EXP is exposed from the notch portionNT provided in the emitter wiring EWL. On the other hand, the coveredportion CVP is covered by the emitter wiring EWL and functions as afield plate portion. Specifically, the side S1 of the base region BRforms a boundary line of a pn junction and the breakdown voltage of theexposed portion EXP is lower than the breakdown voltage of the coveredportion CVP. In other words, the breakdown voltage of the coveredportion CVP is higher than the breakdown voltage of the exposed portionEXP.

As a result, in the electrostatic protection element CB according to thefirst embodiment, for example, when a plus surge charge enters the inputterminal IN electrically coupled to the collector wiring CWL and therebya voltage greater than or equal to the reverse junction breakdownvoltage is applied between the collector region CR (epitaxial layer EPI)and the base region BR, a leakage current occurs at the pn junction ofthe exposed portion EXP of the facing portion FP. As a result, a regionR1 of the base region BR which includes the exposed portion EXPfunctions as a leakage current generation region and a region R2including the covered portion CVP functions as a resistance region RR2.Further, a region filled with oblique lines in the base region BRfunctions as a resistance region RR2. Therefore, in the electrostaticprotection element CB according to the first embodiment, the emitterregion ER and the base region BR are electrically coupled togetherthrough the resistance region RR2. As a result, in FIG. 7B, the leakagecurrent shown in FIG. 3B flows in a current path of (input terminalIN)→collector wiring CWL→plug PLG1→collector region CR→epitaxial layerEPI→exposed portion EXP→base region BR→resistance region RR2 includingthe covered portion CVP→plug PLG3→emitter wiring EWL→(ground terminalGND).

In summary, the electrostatic protection element CB according to thefirst embodiment includes a bipolar transistor where the base region BRand the emitter region ER are electrically coupled together through theresistance region RR2. In particular, the electrostatic protectionelement CB according to the first embodiment has the base region BRformed in the epitaxial layer EPI, the emitter region ER which is formedin the epitaxial layer EPI and contained in the base region BR in planview, and the collector region CR which is formed in the epitaxial layerEPI and separately arranged from the base region BR in plan view.Further, the electrostatic protection element CB according to the firstembodiment includes the emitter wiring EWL which is electrically coupledwith each of the base region BR and the emitter region ER and partiallyoverlapped with the base region BR in plan view. At this time, the baseregion BR has the side S1 including the facing portion FP facing thecollector region CR, and the facing portion FP of the side S1 is formedof the exposed portion EXP that is exposed from the emitter wiring EWLin plan view and the covered portion CVP that is covered by the emitterwiring EWL in plan view.

Next, FIG. 8 is a cross-sectional view taken along line A-A in FIG. 7B.

As shown in FIG. 8, the epitaxial layer EPI made of an n-typesemiconductor layer is formed over the semiconductor substrate 1S, andthe collector region CR made of an n-type semiconductor region is formedin a part of the surface region of the epitaxial layer EPI. In theepitaxial layer EPI, the base region BR made of a p-type semiconductorregion is formed in a part of the surface region separated from thecollector region CR, and the emitter region ER made of an n-typesemiconductor region is formed so as to be contained in the base regionBR.

An interlayer insulating film IL made of, for example, a silicon oxidefilm is formed over the epitaxial layer EPI. In the interlayerinsulating film IL, the plug PLG1 that penetrates the interlayerinsulating film IL and reaches the collector region CR is formed, andthe plug PLG2 that penetrates the interlayer insulating film IL andreaches the emitter region ER is formed. Further, over the interlayerinsulating film IL, the collector wiring CWL and the emitter wiring EWLare formed. The collector wiring CWL is electrically coupled with thecollector region CR through the plug PLG1. On the other hand, theemitter wiring EWL is electrically coupled with the emitter region ERthrough the plug PLG2. The notch portion NT is formed at an end portionof the emitter wiring EWL and a part of the base region BR is exposedfrom the emitter wiring EWL.

Subsequently, FIG. 9 is a cross-sectional view taken along line B-B inFIG. 7B.

As shown in FIG. 9, the base region BR is formed in a part of thesurface region of the epitaxial layer EPI formed over the semiconductorsubstrate 1S. The interlayer insulating film IL is formed over theepitaxial layer EPI in which the base region BR is formed. In theinterlayer insulating film IL, the plug PLG3 that penetrates theinterlayer insulating film IL is formed. Over the interlayer insulatingfilm IL, the emitter wiring EWL is formed. The emitter wiring EWL iselectrically coupled with the base region BR through the plug PLG3. Atthis time, the base region BR has the region R1 exposed from the emitterwiring EWL and the region R2 covered by the emitter wiring EWL, and aregion (a region filled with dots) which includes the region R2 of thebase region BR and is formed in a position close to the plug PLG3functions as the resistance region RR2. In the way described above, theelectrostatic protection element CB according to the first embodiment isformed.

Characteristic of First Embodiment

Next, a characteristic point of the first embodiment will be described.The characteristic point of the first embodiment is, for example, asshown in FIG. 7B, to provide the exposed portion EXP that is exposedfrom the emitter wiring EWL and the covered portion CVP that is coveredby the emitter wiring EWL in the facing portion FP of the base region BRfacing the collector region CR. Thereby, according to the electrostaticprotection element CB of the first embodiment, it is possible to causethe voltage determined by the product of the resistance value of theresistor R and the current value of the leakage current flowing throughthe resistor R (see FIG. 3B) to easily reach the snapback voltage.Thereby, it is possible to improve the performance of the electrostaticprotection element CB.

Hereinafter, the point that it is possible to cause the voltagedetermined by the product of the resistance value of the resistor R andthe current value of the leakage current flowing through the resistor R(see FIG. 3B) to easily reach the snapback voltage according to thecharacteristic point of the first embodiment will be described.

First, the collector region CR is formed of an n-type semiconductorregion and the epitaxial layer EPI is also formed of an n-typesemiconductor layer. On the other hand, the base region BR is formed ofa p-type semiconductor region. Thus, in FIG. 7B, a pn junction is formedat the side S1 of the base region BR that is in contact with theepitaxial layer EPI. In particular, when focusing on the facing portionFP facing the collector region CR, both of the exposed portion EXP andthe covered portion CVP of the facing portion FP form the boundary lineof the pn junction.

At this time, the reverse junction breakdown voltage of the coveredportion CVP is higher than that of the exposed portion EXP. The reasonof this will be described below.

For example, the collector wiring CWL shown in FIG. 7B is coupled withthe input terminal IN shown in FIG. 1 and it is assumed that a plussurge charge enters the input terminal IN. In this case, a positivepotential is applied to the collector region (n-type semiconductorregion) CR that is electrically coupled with the collector wiring CWL. Apositive potential is also applied to the epitaxial layer EPI formed ofa semiconductor layer having the same conductivity type as that of thecollector region CR. On the other hand, the emitter wiring EWL shown inFIG. 7B is coupled with the ground terminal GND shown in FIG. 1. Asshown in FIG. 7B, the emitter wiring EWL shown in FIG. 7B iselectrically coupled with the base region BR through the plug PLG3.Thus, when a plus surge charge enters the input terminal IN, a reversebias is applied to the pn junction formed at a boundary region (the sideS1) between the base region BR and the epitaxial layer EPI. As a result,a depletion layer extending toward the epitaxial layer EPI and adepletion layer extending toward the base region BR are formed from bothof the exposed portion EXP and the covered portion CVP that form thefacing portion FP of the side S1.

Here, the width of the depletion layer extending toward the epitaxiallayer EPI from the covered portion CVP is greater than the width of thedepletion layer extending toward the epitaxial layer EPI from theexposed portion EXP. This is because a planar overlapping portion isformed between the emitter wiring EWL and the epitaxial layer EPI in thecovered portion CVP covered by the emitter wiring EWL as shown in FIG.7B. Specifically, the emitter wiring EWL is coupled to the groundterminal GND, so that a relatively negative potential is applied to theemitter wiring EWL with respect to the epitaxial layer EPI to which apositive potential is applied. In this case, electrons present in theepitaxial layer EPI planarly overlapping with the emitter wiring EWL arebrought away from the emitter wiring EWL by the relative negativepotential applied to the emitter wiring EWL. This means that thedepletion layer extends into the epitaxial layer EPI planarlyoverlapping with the emitter wiring EWL. That is, in the covered portionCVP, the depletion layer extends into the epitaxial layer EPI planarlyoverlapping with the emitter wiring EWL, so that the width of thedepletion layer extending toward the epitaxial layer EPI from thecovered portion CVP is greater than the width of the depletion layerextending toward the epitaxial layer EPI from the exposed portion EXPthat does not planarly overlap with the emitter wiring EWL. When thewidth of the depletion layer becomes large, the reverse junctionbreakdown voltage of the pn junction becomes large, so that the reversejunction breakdown voltage of the covered portion CVP becomes higherthan that of the exposed portion EXP according to the characteristicpoint of the first embodiment.

Thereby, according to the electrostatic protection element CB of thefirst embodiment, the pn junction of the exposed portion EXP is brokendown by a reverse bias lower than that of the pn junction of the coveredportion CVP. This means that only the exposed portion EXP functions as acurrent path of leakage current. Specifically, although the related artshown in FIG. 4B uses the entire facing portion FP facing the collectorregion CR as the current path of the leakage current, the firstembodiment uses only the exposed portion EXP of the facing portion FPfacing the collector region CR as the current path of the leakagecurrent as shown in FIG. 7B. In other words, in the first embodiment,the covered portion CVP of the facing portion FP facing the collectorregion CR is used as a part of the resistance region RR2 instead of thecurrent path of the leakage current. Thereby, according to theelectrostatic protection element CB of the first embodiment, it ispossible to adjust each of the resistance value of the resistor R andthe current value of the leakage current flowing through the resistor Rin a good balance. As a result, it is possible to cause the voltagedetermined by the product of the resistance value of the resistor R andthe current value of the leakage current flowing through the resistor Rto easily reach the snapback voltage. In this way, according to theelectrostatic protection element CB of the first embodiment, it ispossible to improve performance. In other words, the technical idea ofthe first embodiment is not an idea of using the entire facing portionFP facing the collector region CR as the current path of the leakagecurrent as in the related art shown in FIG. 4B, but a technical idea ofproviding a portion used as the current path of the leakage current anda portion used as a part of the resistance region in the facing portionFP facing the collector region CR. The technical idea of the firstembodiment is embodied as the characteristic point of the firstembodiment in which a portion with a high reverse junction breakdownvoltage and a portion with a low reverse junction breakdown voltage areintentionally provided in the facing portion FP facing the collectorregion CR and thereby the portion with a high reverse junction breakdownvoltage is used as a part of the resistance region RR2 and the portionwith a low reverse junction breakdown voltage is used as the currentpath of the leakage current. Specifically, in the first embodiment, asshown in FIG. 7B, a portion with a high reverse junction breakdownvoltage and a portion with a low reverse junction breakdown voltage areintentionally provided in the facing portion FP facing the collectorregion CR by forming the exposed portion EXP that is exposed from theemitter wiring EWL and the covered portion CVP that is covered by theemitter wiring EWL. In this case, according to the characteristic pointof the first embodiment, it is possible to adjust each of the resistancevalue of the resistor R and the current value of the leakage currentflowing through the resistor R in a good balance by well adjusting aratio between the exposed portion EXP and the covered portion CVP. As aresult, according to the characteristic point of the first embodiment,it is possible to cause the voltage determined by the product of theresistance value of the resistor R and the current value of the leakagecurrent flowing through the resistor R to easily reach the snapbackvoltage.

The characteristic point of the first embodiment will be qualitativelydescribed in an easily understandable way. For example, it is assumedthat the snapback voltage when the state shown in FIG. 3B changes to thestate shown in FIG. 3C is “60”. At this time, in the related art shownin FIG. 4B, the entire facing portion FP facing the collector region CRis used as the current path of the leakage current, so that it isassumed that, for example, the resistor R is “5” and the leakage currentis “10” in the state shown in FIG. 3B. In this case, in the related art,the voltage determined by the product of the current value of theleakage current and the resistance value of the resistor R is “50” whichis lower than the snapback voltage (“60”), so that the electrostaticprotection element does not snap back.

On the other hand, in the first embodiment shown in FIG. 7B, the currentpath of the leakage current is not the entire facing portion FP facingthe collector region CR, but the entire exposed portion EXP. Therefore,the leakage current is smaller than that in the related art (½ of therelated art). For example, the leakage current is “5”. On the otherhand, in the first embodiment, the covered portion CVP of the facingportion FP functions as a part of the resistance region RR2, so that theresistance value of the resistor R is greater than that in the relatedart (2.5 times of the related art). For example, the resistance value ofthe resistor R is “12.5”. In this case, in the first embodiment, thevoltage determined by the product of the current value of the leakagecurrent and the resistance value of the resistor R is “62.5” which isgreater than the snapback voltage “60”, so that the electrostaticprotection element snaps back.

In the example described above, while the voltage (“50”) determined bythe product of the current value of the leakage current and theresistance value of the resistor R is lower than the snapback voltage(“60”) in the related art, the voltage (“62.5”) determined by theproduct of the current value of the leakage current and the resistancevalue of the resistor R is higher than the snapback voltage (“60”) inthe first embodiment.

This means that the electrostatic protection element CB according to thefirst embodiment snaps back more easily than the electrostaticprotection element CB1 according to the related art. That is, it ispossible to improve the performance of the electrostatic protectionelement CB according to the characteristic point of the firstembodiment.

In particular, in the first embodiment, as shown in FIG. 7B, the plugPLG3 that electrically couples the base region BR and the emitter regionEWL together is arranged in an end portion region of one end portion ofthe base region BR covered by the emitter wiring EWL. Thereby, accordingto the first embodiment, due to a synergistic effect of using thecovered portion CVP of the facing portion FP facing the collector regionCR as a part of the resistance region RR2, it is possible to increasethe resistance value of the resistance region RR2 without increasing thesize of the base region BR.

Further, according to the characteristic point of the first embodiment,not only it is possible to merely improve the performance of theelectrostatic protection element CB, but also it is possible to obtain aremarkable effect that it is possible to improve the performance of theelectrostatic protection element CB without causing a disadvantage ofincreasing the size of the electrostatic protection element CB and adisadvantage of requiring much labor and time for the design change.

Hereinafter, the above remarkable effect will be described. For example,in the related art shown in FIG. 4B, it is difficult to further increasethe leakage current because the entire facing portion FP of the baseregion BR facing the collector region CR has been used as a portionwhere the leakage current occurs. For this reason, in the related art,it is considered to increase the resistance value of the resistor R inorder to cause the voltage determined by the product of the currentvalue of the leakage current and the resistance value of the resistor Rto easily reach the snapback voltage. However, this means that the sizeof the resistance region RR1 shown in FIG. 4B is increased, and thismeans that the size of the protruding portion PTP of the base region BRshown in FIG. 4A is increased. In this case, the size of theelectrostatic protection element CB1 according to the related artincreases. Further, changing the size of the base region BR itself meansthat a design of a semiconductor area that is formed into asemiconductor substrate must be changed from the beginning, so that muchlabor and time are required. Therefore, in the related art, from aviewpoint of improving the performance of the electrostatic protectionelement CB1, when making a design change to cause the voltage determinedby the product of the resistance value of the resistor R and the currentvalue of the leakage current flowing through the resistor R to easilyreach the snapback voltage, the disadvantage of increasing the size ofthe electrostatic protection element CB1 and the disadvantage ofrequiring much labor and time for the design change become apparent.

On the other hand, in the first embodiment, as shown in FIG. 7B, thevoltage determined by the product of the resistance value of theresistor R and the current value of the leakage current flowing throughthe resistor R is caused to easily reach the snapback voltage by formingthe exposed portion EXP that is exposed from the emitter wiring EWL andthe covered portion CVP that is covered by the emitter wiring EWL in thefacing portion FP facing the collector region CR. Such a design changecan be performed by only changing a layout pattern of the emitter wiringEWL. In other words, it is possible to adjust a ratio between theexposed portion EXP that is exposed from the emitter wiring EWL and thecovered portion CVP that is covered by the emitter wiring EWL by onlychanging the layout pattern of the emitter wiring EWL.

This means that it is possible to increase the size of the resistanceregion RR2 by the covered portion CVP without increasing the size of theprotruding portion PTP of the base region BR shown in FIG. 7A accordingto the first embodiment. Therefore, in the design change according tothe first embodiment, it is not necessary to increase the size of theelectrostatic protection element CB to cause the voltage determined bythe product of the resistance value of the resistor R and the currentvalue of the leakage current flowing through the resistor R to easilyreach the snapback voltage. The design change according to the firstembodiment can be performed by only changing the layout pattern of theemitter wiring EWL without changing the size of the base region BRformed in the semiconductor substrate. At this time, a design change ofthe layout pattern of the emitter wiring EWL requires less labor andtime as compared with a design change of the base region BR formed inthe semiconductor substrate and can be relatively easily performed.

Thus, according to the first embodiment, when making a design change tocause the voltage determined by the product of the resistance value ofthe resistor R and the current value of the leakage current flowingthrough the resistor R to easily reach the snapback voltage, it ispossible to improve the performance of the electrostatic protectionelement CB without actualizing the disadvantage of increasing the sizeof the electrostatic protection element CB and the disadvantage ofrequiring much labor and time for the design change. As described above,it is known that the characteristic point of the first embodiment is auseful technical idea because not only it is possible to improve theperformance of the electrostatic protection element CB but also it ispossible to realize improvement of the performance of the electrostaticprotection element CB without actualizing the disadvantages that becomeapparent in the technical idea of the related art.

Second Embodiment

<Device Structure of Electrostatic Protection Element>

FIGS. 10A and 10B are diagrams showing a device structure of anelectrostatic protection element CB according to a second embodiment. Inparticular, FIG. 10A is a schematic plan view showing components formedin a semiconductor substrate among components of the electrostaticprotection element CB according to the second embodiment. FIG. 10B is aschematic plan view further showing components including also a wiringlayer formed over the semiconductor substrate among the components ofthe electrostatic protection element CB according to the secondembodiment.

In FIG. 10A, the electrostatic protection element CB according to thesecond embodiment includes a base region BR having a side S1, an emitterregion ER contained in the base region BR in plan view, and a collectorregion CR having a side S2 in parallel with the side S1. At this time,the length of the side S1 of the base region BR is the same as thelength of the side S2 of the collector region CR.

Next, as shown in FIG. 10B, in the electrostatic protection element CBaccording to the second embodiment, the length of the side S1 of thebase region BR is the same as the length of the side S2 of the collectorregion CR, so that the entire side S1 of the base region BR is a facingportion FP facing the collector region CR. The facing portion FP facingthe collector region CR includes an exposed portion EXP that is exposedfrom an emitter wiring EWL in plan view and a covered portion CVP thatis covered by the emitter wiring EWL in plan view. The electrostaticprotection element CB according to the second embodiment is formed asdescribed above.

Characteristic of Second Embodiment

Subsequently, a characteristic point of the second embodiment will bedescribed. The characteristic point of the second embodiment is, forexample, as shown in FIG. 10A, that the length of the side S1 of thebase region BR is the same as the length of the side S2 of the collectorregion CR and the exposed portion EXP and the covered portion CVP areprovided on the side S1. Thereby, according to the electrostaticprotection element CB of the second embodiment, for example, it ispossible to reduce a plane size of the electrostatic protection elementCB to a size smaller than a plane size of the electrostatic protectionelement CB according to the first embodiment while maintaining the sameor higher performance than that of the electrostatic protection elementCB according to the first embodiment shown in FIG. 7A.

In the electrostatic protection element CB according to the secondembodiment, for example, as shown in FIG. 10B, the exposed portion EXPand the covered portion CVP are formed on the side S1, a region R1including the exposed portion EXP functions as a current path of leakagecurrent, and a region R2 including the covered portion CVP functions asa resistance region RR3. Thus, in the electrostatic protection elementCB according to the second embodiment, it is not necessary to providethe protruding portion PTP to secure the resistance region RR2 as in theelectrostatic protection element CB according to the first embodimentshown in FIGS. 7A and 7B. That is, in the electrostatic protectionelement CB according to the second embodiment, the resistance region RR3is secured in the region R2 that includes the covered portion CVP, sothat it is possible to exert the same or higher performance than that ofthe electrostatic protection element CB according to the firstembodiment even when the protruding portion PTP is not provided.

As a result, according to the electrostatic protection element CB of thesecond embodiment, it is possible to obtain a remarkable effect that theplane size of the electrostatic protection element CB can be reducedwhile realizing a performance higher than or equal to that of theelectrostatic protection element CB of the first embodiment where thevoltage determined by the product of the resistance value of theresistor R and the current value of the leakage current flowing throughthe resistor R (see FIG. 3B) easily reaches the snapback voltage.

<Modified Example>

Next, an electrostatic protection element CB according to a modifiedexample will be described. FIG. 11 is a cross-sectional view showing aschematic device structure of the electrostatic protection element CBaccording to the modified example. As shown in FIG. 11, in theelectrostatic protection element CB according to the modified example, aconductor film CF is formed between a base region BR and an emitterwiring EWL in a cross-sectional view, and a covered portion CVP iscovered by the conductor film CF. At this time, the conductor film CF isformed so as to cross over a pn junction formed at a boundary regionbetween the base region BR and an epitaxial layer EPI. The conductorfilm CF is electrically coupled with the emitter wiring EWL by a plugPLG4 that penetrates an interlayer insulating film IL. As a result, inthe modified example, not only the emitter wiring EWL but also theconductor film CF functions as a field plate portion that increases thereverse junction breakdown voltage of the pn junction at the coveredportion CVP.

In particular, in the modified example, the conductor film CF is formedso as to be directly in contact with the pn junction formed at theboundary region between the base region BR and the epitaxial layer EPI,so that it is possible to increase the width of a depletion layerextending from the conductor film CF into the epitaxial layer EPI, andthereby, according to the modified example, it is possible to increasethe reverse junction breakdown voltage of the pn junction at the coveredportion CVP. Further, when the conductor film CF is formed of a p-typesemiconductor film represented by a p-type polysilicon film, a pnjunction is formed between the conductor film CF and the epitaxial layerEPI along with the effect described above and a reverse bias is alsoapplied to the pn junction. Therefore, it is possible to further extendthe depletion layer in the epitaxial layer EPI. Thereby, according tothe modified example, it is possible to increase a difference betweenthe reverse junction breakdown voltage of the exposed portion EXP andthe reverse junction breakdown voltage of the covered portion CVP.Therefore, according to the modified example, it is possible to causethe covered portion CVP to reliably function as a resistance regionwhile the exposed portion is used as a current path of the leakagecurrent.

While the invention made by the inventors has been specificallydescribed based on the embodiments, it is needless to say that thepresent invention is not limited to the embodiments and may be variouslymodified without departing from the scope of the invention.

What is claimed is:
 1. A semiconductor device comprising: anelectrostatic protection element including a bipolar transistor, whereinthe electrostatic protection element includes: a base region formed inan epitaxial layer, an emitter region which is formed in the epitaxiallayer and contained in the base region in plan view, a collector regionwhich is formed in the epitaxial layer and separately arranged from thebase region in plan view, and an emitter wiring which is electricallycoupled with each of the base region and the emitter region andpartially overlapped with the base region in plan view, wherein the baseregion and the emitter region are electrically coupled together througha resistance region, wherein the base region has a first side includinga facing portion that faces the collector region, and wherein the facingportion of the first side includes: an exposed portion that is exposedfrom the emitter wiring in plan view, and a covered portion that iscovered by the emitter wiring in plan view.
 2. The semiconductor deviceaccording to claim 1, wherein the exposed portion is exposed from anotch portion provided in the emitter wiring.
 3. The semiconductordevice according to claim 1, wherein the covered portion functions as afield plate portion.
 4. The semiconductor device according to claim 1,wherein the first side forms a boundary line of a pn junction, andwherein a breakdown voltage of the exposed portion is lower than abreakdown voltage of the covered portion.
 5. The semiconductor deviceaccording to claim 1, wherein the base region includes: a first regionincluding the exposed region, and a second region including the coveredportion, wherein the first region functions as a leakage currentgeneration region, and wherein the second region functions as theresistance region.
 6. The semiconductor device according to claim 1,wherein the first side includes: a first end portion that is covered bythe emitter wiring in plan view, and a second end portion that isexposed from the emitter wiring in plan view, and wherein a plug thatelectrically couples the base region and the emitter region together isformed in an end portion region of the base region including the firstend portion of the first side.
 7. The semiconductor device according toclaim 1, wherein the collector region has a second side in parallel withthe first side of the base region, and wherein a length of the firstside of the base region is the same as a length of the second side ofthe collector region.
 8. The semiconductor device according to claim 1,wherein a conductor film is formed between the base region and theemitter wiring in a cross-sectional view, and wherein the coveredportion is covered by the conductor film.
 9. The semiconductor deviceaccording to claim 8, wherein the conductor film is formed of apolysilicon film.
 10. The semiconductor device according to claim 1,wherein the base region is formed of a p-type semiconductor region,wherein each of the emitter region and the collector region is formed ofan n-type semiconductor region, and wherein the epitaxial layer isformed of an n-type semiconductor layer.
 11. The semiconductor deviceaccording to claim 1, further comprising: an input terminal to which asignal is inputted; a power supply terminal to which a power supplypotential is supplied; a ground terminal to which a reference potentialis supplied; and wherein the electrostatic protection element is coupledbetween the input terminal and the ground terminal.
 12. Thesemiconductor device according to claim 11, wherein the bipolartransistor is an NPN bipolar transistor, wherein the collector region iselectrically coupled with the input terminal, and wherein the emitterregion is electrically coupled with the ground terminal.